Toru Miki

Harmonic source identification by simultaneous-multipoint harmonic measurements

An identification of a harmonic source from voltage harmonics measured at outlets in a university campus is reported in this paper. A result obtained by a wide-area measurement shows that the major harmonic source is in a building. Another measurement is carried out within a building, and a rectification circuit is identified as a harmonic source. Each measured result is obtained by simultaneous-multipoint measurements using instruments developed by the authors. The harmonic voltages are determined by the current of the harmonic source and the line impedance of e distribution system. The location of the harmonic source is identified only from the voltages at outlets if a small voltage difference caused by the line impedance can be detected. The measured results clearly show the satisfactory accuracy and the effectiveness of the proposed instrument. The harmonic current ratio of the load is obtained from the voltage ratio between the voltage harmonics and the line impedance. The type of the load can be estimated from the measured harmonic voltage with a simple instrument for measuring a line-impedance developed by authors, because the current ratio is unique to each load.

Reproduction of electromagnetic field waveforms and tower currents associated with return strokes struck Tokyo Skytree

Observation of lightning current by using Rogowski coils started in February 2012 at Tokyo Skytree, which is a 634-m high freestanding broadcasting tower. Electromagnetic field waveforms are also observed by capacitive antennas at several tens of kilometers from the tower. Lightning current and electric field waveforms simultaneously observed in May 2012 are reproduced by using an electromagnetic model of a return stroke with the help of NEC-4. Observed lightning current waveforms are well reproduced by modeling the tower with small number of thin wires. Electromagnetic field waveforms also are reproduced by an inclined lightning channel model reconstructed from still photographs.

Upward and downward lightning observed at Tokyo Skytree

This paper describes observations of lightning current waveform at Tokyo Skytree, which stands in the eastern area of central Tokyo, located in the Kanto Plain, and is a 634-m high freestanding broadcasting tower. Direct observation of lightning current by using a pair of Rogowski coils started in the end of February 2012. From 2012 to the end of 2013, currents associated with 24 lightning flashes which hit the tower were recorded. In 2012, most of the flashes were upward as was expected; however, in 2013, most of the flashes observed in summer were downward. We have also evaluated statistical characteristics of obtained lightning current waveforms.